I am trying to explain endergonic and exergonic reactions to my 10th grade AP Biology Class. I have a list of examples (eg. Photosynthesis, Chemical Reactions) but I really want to give them a very simple example. Does that make sense? I just want to be able to break it down further because I feel like they are having a hard time with it. Thanks for any advice!!

I like those instant-cold packs for sports injuries. They contain a salt that undergoes endergonic dissolution, so you break the inner pouch and the pack gets cold. That makes a nice hands-on demo of an endergonic process and is not dreadfully expensive.

that would demonstrate exothermic/endothermic rather than exergonic/endergonic. I am afraid there is no simple way to show exergonic/endergonic reactions since deltaG is a quantitative sum of enthalpy and entropy. Maybe an explosion would be the best example of an exergonic reaction because it releases heat and increases entropy. Lighting a match might be a substitute for that, because blowing up grenades in your classroom might not be the best idea. As for an endergonic process, you would need something that takes up heat and decreases entropy.

"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

Endergonic: The sponge absorbs the water (ie, energy) and now carries that energy, and can be expelled.

Exergonic: *Squeeze sponge* energy leaves the system (ie, sponge) and the sponge is no longer any good for scrubbing. Also, the water would normally leave the sponge of its own accord, but if you (an enzyme) squeeze the sponge, reactions occur much faster.